The present invention relates to a new and improved construction of a regulation system for a steam turbine installation which is of the type comprising a steam generator and a multi-stage turbine installation or turbine including a high-pressure stage, and wherein the regulation system comprises a regulation valve arranged between the steam generator and the high-pressure stage of the turbine and a by-pass valve connected in parallel with said high-pressure stage, there also being provided control devices with associated control circuits for such valves.
In systems of the aforementioned general arrangement the by-pass valve is primarily provided for the purpose of admitting additional steam to the intermediate- and low- pressure stages in the presence of an overload and at the operating range around full load.
To obtain good efficiency for the regulation valve the dimensions thereof must be properly accommodated to those of the turbine installation, in order that the regulation valve, during full load, exhibits a small throttling action and thus only has small throttling losses. Yet, due to these measures there is however present at the full load range poor regulation characteristics, i.e. slow regulation, due to the flat regulation characteristics of the regulation valve with low throttling.